K. Tagami

Chemical stability and microstucture on sputtered CoCr perpendicular media

Chemical stabilities, especially corrosion characteristics for sputtered CoCr perpendicular recording media have been investigated. The corrosions were analyzed by XPS and by measuring electrical resistance increase (ΔR/R 0 ) for a CoCr film stripe pattern under exposure to 80°C and 85 % relative humidity. The corrosion rate strongly depended on the CoCr film preparation conditions. The correlation between ΔR/R 0 and test time t was expressed by the equation \DeltaR/R_{0} = \alpha \log (t + 1) , where α was a coefficient. In the regions of low sputtering pressure and high power, excellent corrosion resistances were obtained. These corrosion characteristics were attributed to the crystalline microstructures.

A new preparation method for γ-Fe 2 O 3 thin film recording media through direct sputtering of Fe 3 O 4 thin films

A new preparation method for γ-Fe 2 O 3 thin film recording media has been established. Using sintered Fe 3 O 4 plates as targets, Fe 3 O 4 films are directly formed over wide sputtering condition ranges through R.F. sputtering in argon atmosphere. Planar magnetron sputtering has successfully been attempted to attain sputtering rates higher than 2,000 A/min. Co, Cu doped γ-Fe 2 O 3 thin film disks have been prepared by the present method. Their read/write characteristics were experimentally evaluated using a conventional ferrite head with 20 μm core width, which has shown D -6dB density as high as 1140 BPM (bits per millimeter).

Ta additive effect on RF magnetron sputtered CoCr films

Magnetic properties for sputtered CoCrTa films (18 at.% Cr and 2.0-3.0 at.% Ta), which were deposited under various background pressures P/sub i/, and argon sputtering pressures, P/sub Ar/, have been examined. The perpendicular anisotropy field H/sub k/ for CoCrTa films maintains high values of 5-6 kOe in a wide range of P/sub i/ and P/sub Ar/, as compared with that for CoCr films. In order to optimize Ta composition, magnetic properties and crystalline microstructures for Ta additive content (0-4.0 at.%) have been investigated. H/sub k/ and perpendicular coercivity H/sub c perpendicular to / increase with increasing Ta concentration above 2.0 at.% Ta. C-axis orientation is improved by adding Ta to CoCr films. However, above 3.0 at.% Ta, H/sub c perpendicular to / steeply decreases and domain wall motion is observed, owing to the increase in crystalline grain size. The appropriate Ta composition is 2.0-3.0 at.%. >

Analysis of track-edge noise in thin-film recording media

Track-edge noise has been analyzed to clarify track-edge noise mechanisms. Edge noise arises from two different regions: the bit edge where the magnetization direction is opposite to the previously dc-erased direction and the magnetic transition edge. The edge noise at low density is mainly due to the magnetic distribution at the bit edge. The transition edge noise increases with increasing recording density, and it becomes dominant at high-recording density for an oriented medium. On the other hand, the transition edge noise is almost constant with increasing recording density for an isotropic medium.

Corrosion rate activation energy of sputtered CoCr perpendicular media

Corrosion rate activation energy ΔE has been evaluated by measuring electrical resistance increase due to corrosion for CoCr (0 ∼ 26 at%Cr) film stripe patterns under exposure to various temperatures and 85% relative humidity. A relation of corrosion layer thickness X to Cr density x, test temperature T and test time t were obtained. The relation was expressed by X = C \cdot \exp(-\gamma \cdot x) \cdot \exp(-\Delta E/k T)\cdot \log(t+l) , where K, γ and C are the coefficient and Boltzmanns constant,respectively. ΔE values for CoCr films (0∼ 26 at%Cr) depend upon Cr density and preparation conditions. These values ranged from 0.075 to 0.32 eV. Corrosion characteristics are varied by not only film microstructure, but also to Cr atom distribution in crystalline matrix even for films with same Cr density.

Overwrite temperature dependence for magnetic recording

The temperature effect on overwrite (OW) characteristics for magnetic recording, using various heads and media, has been examined. Overwrites depend linearly on the difference (T2−T1) between overwrite temperature T2 and previous recording temperature T1. Their gradients vary from −0.10 to 0.43 dB/deg, depending on head‐media combinations. The gradients are proportional to the difference (αBs−αHc), between temperature coefficient for head saturation magnetic flux density Bs and that for media coercivity Hc. Therefore, temperature dependence of overwrite is reduced by selecting a mead‐media combination with a small ‖αBs−αHc‖ value. This relation is explained by temperature variation in recording depth.

Pass wear resistance for perpendicular recording media

Pass wear resistance of sputtered CoCr perpendicular flexible disks has been investigated. The disk was composed of CoCr film on a heat-resistant base film, a protection layer, and lubricant. The pass wear durabilities were evaluated for a conventional double-sided 3.5-in drive. It was found that the scratch depth (SD) per load force (LF) depends on preparation conditions, and that the CoCr film hardness is related to pass wear durability. SD/LF values range from 0.2 to 0.3 for CoCr films without a protective layer. With a protective layer and lubricant, the range of SD/LF values varies from 0.2-0.3 to 0.1-0.3. The disk hardness, especially for small SD/LF media, has been improved. A pass wear durability of 30 million passes was attained for a disk having SD/LF=0.1. >

Noise characteristics in Co‐Cr perpendicular recording media

Noise characteristics in Co‐Cr and Co‐Cr/Ni‐Fe perpendicular recording media were theoretically analyzed, based on an uncorrelated particle magnetization model. The analyzed results were compared with experimental results. Marked differences in noise spectra were found between single layer and double layer media, especially in the long wavelength region. The measured noise and signal spectra in a Co‐Cr/Ni‐Fe double layer medium were close to the numerically analyzed values for perpendicular magnetization, rather than for longitudinal magnetization. This indicates that the magnetization in the Co‐Cr layer is directed almost perpendicularly. Furthermore, the measured noise power decreased with increasing the medium perpendicular anisotropy, which is closely related to the medium crystal orientation. As a conclusion, noise from Co‐Cr perpendicular recording media is attributed to the medium grain magnetization direction dispersion, where the magnetizations are almost perpendicular to the medium surface.

Ferrite thin film disks using electroless-plated Ni-P substrates

Ferrite thin film disks using electroless-plated Ni-P substrates have been prepared. The practicability of attaining these disks at areal densities above 4.7 X l04bits/mm2(28 K-FRPI X 1100 TPI) has been confirmed from the following view points: read/write and error characteristics, signal-to-noise ratio (SNR), and wear durabilities. Over -20 K-FRPI, noise level decreases were found. As a result, more than SNR 35 dB at 40-50 K-FRPI were attained. Practical feasibilities were also confirmed at 40-50 K-FRPI. In wear durability, 20 000 contact-start-stop operations were achieved.

Offtrack characteristics on media noise for Co-Cr-Ta films

The effect of remanent magnetic flux density (B/sub r/) and magnetic layer thickness (/spl delta/) on offtrack noise characteristics in Co-Cr-Ta alloy thin films is investigated. It has been found that decreasing the value of B/sub r/ is a more effective method of improving offtrack noise characteristics than decreasing the value of /spl delta/. Offtrack noise is shown to be due to the fluctuations in the amplitude of readback waveforms, fluctuations which are caused by fluctuations in magnetic transition amplitude. It was observed, using a magnetic force microscope, that lower B/sub r/ media had sharp boundaries at the track edge regions and the magnetization was more uniform, compared with those of higher B/sub r/ media.